NoClassDefFoundError when executing from client

I'm getting NoClassDefFoundError: AcmeXMLHelper where AcmeXMLHelper is
the app. on the server which I'm trying to run from AcmeClient.
The client starts AcmeSessionBean fine, but when AcmeSessionBean tries to
instantiate AcmeXMLHelper, it fails.
Could anyone give me some ideas on where to look for the problem.

AcmeSessionBean.java:
package ejb;
....
import xmlhelper.AcmeXMLHelper;
public class AcmeSessionBean implements SessionBean {
....
    public String getProduct(in productID) {
        try {
            System.out.println("starting Bean method");
            AcmeXMLHelper axh = new AcmeXMLHelper(); // exception occurs
            System.out.println("got AcmeXMLHelper");
            return axh.getProductXMLasString(productID);
        } catch (Exception e) {
            throw new EJBException(e.getMessage());
        }
    }
    ...

my files are:
serverclasses/xmlhelper/AcmeXMLHelper.class
clientclasses/xmlhelper/AcmeXMLHelper.class
ejb/AcmeSessionBean.class in statelessjb.jar in autodeploy/statelessjb.ear
clientclasses/ejb/AcmeClient.class
plus more...